(a) Field of the Invention
This invention relates to textile material for use as the outer shell fabric of a firefighter garment. More particularly, the invention is concerned with a lightweight outer shell fabric that is constructed of two different homogeneous yarn types in such a way as to increase resistance to mechanical and UV degradation while increasing thermal protective performance. In addition, the textile material can stretch, thereby increasing comfort and mobility.
(b) Description of Prior Art
All fabrics used in the manufacture of protective clothing for firefighters must satisfy minimum performance requirements for flame, heat and tear resistance as prescribed by the National Fire Protection Agency (NFPA).
A firefighter garment is normally made of a composite layer of materials including an outer shell fabric. All fabrics currently used for the outer shell fabric of firefighter garments are woven. The warps and wefts of the outer shell fabric usually comprise spun yarns that are either made up of homogeneous fibers or intimate blends of different fibers. The purpose of using intimate blends of fibers in yarns is to combine the individual strengths of each of the constituent fibers. However, since each fiber has its own weaknesses as well as strengths, the resulting intimate blend yarn must necessarily have some performance compromises as well.
Many of the fibers used in the yarns used in outer shell fabric fabrics of firefighter garments have drawbacks: difficulty in absorbing dye stuffs, poor color retention, UV degradation, fibrillation, poor abrasion resistance.
The fabric may be constructed as a plain, ripstop, twill, herringbone or other traditional weave construction; it will however, appear as a continuous single sheet of yarns. And although there may be a face and a back surface to the weave construction, the face and back surfaces will consist of the identical yarns.
An alternative to spun yarns is multi-filamentary yarns. The latter have a much higher strength-to-weight and strength-to-denier ratios than the spun yarns of similar fibers. They are also more abrasion resistant and less water absorbing than spun yarns of the same fiber.
The principal disadvantages to multi-filamentary yarns are that the resulting fabrics are susceptible to yarn slippage.
The woven fabrics currently used as the outer shell fabric of fire protective garments, whether constituted of spun yarns, multi-filamentary or both, fray and ravel after being torn, cut or punctured. Fraying and raveling not only degrade the appearance of the garment, they make repairs more difficult, and they may increase the risk of injury to the firefighter wearing the garment.
U.S. Pat. No. 5,299,602 discloses an outer shell fabric wherein the textile material comprises warps of alternating multi-filamentary aramid yarns and wefts of alternating spun aramid and multi-filamentary aramid yarns in a twill weave. The object of the invention disclosed in that Patent was to increase firefighter comfort and mobility without reducing mechanical resistance. However, this fabric is still more vulnerable to yarn and seam slippage than fabrics made with 100% spun yarns. Also as a consequence of the high percentage of multi-filamentary yarns, the fabric ravels and frays when cut or torn. Furthermore, the fabric has a preponderance of KEVLAR® (aramid resin by DuPont) yarns on the face surface of the fabric and KEVLAR® is more subject to mechanical and ultraviolet (UV) degradation than either spun or multi-filamentary NOMEX® (yarns or threads of synthetic fibers by DuPont.
U.S. Pat. No. 5,527,597 discloses a woven firefighter fabric that incorporates a core-spun yarn (a LYCRA® (yarns or threads of synthetic fibers by DuPont) core protected by a polybenzimidazole/aramid wrap) to impart a degree of elasticity to the fabric. Although the Patent claims that the fabric maintains its elasticity after five minutes at 500° F., the literature reveals that LYCRA® is not thermally stable in firefighting environments: if stretched at temperatures above 370–390° F., LYCRA® will lose its elasticity; above 415° F., LYCRA® begins to char and lose its properties. Therefore, this stretchable fabric would suffer irreversible degradation in a firefighting environment.
It is therefore an object of the present invention to provide a stretchable fabric wherein the yarns such as aramid yarns would maintain their integrity at temperatures in excess of 600° F.
It is another object of the present invention to provide a textile material for the outer shell fabric of a firefighter garment that is lightweight yet has increased abrasion, tear, and UV resistance.
It is another object of the present invention to provide a textile material for the outer shell fabric of a firefighter garment that has a higher thermal protective performance rating than conventional fabrics of the same weight and fiber type.
It is another object of the present invention to achieve elasticity through the inherent stretchiness of a warp knit construction and not through the introduction of thermally unstable elastomers.
It is a further object of the present invention to provide a warp knit textile material that can be used to produce a firefighter outer shell fabric that is more resistant to fraying and raveling than the currently used woven fabrics.